Mechanical ventilation in patients with SARS-CoV-2 pneumonia

Abstract

The coronavirus (CoV) belongs to a family of viruses that can cause a variety of clinical presentations, including catarrhal symptoms, cough, fever, respiratory distress, and conditions such as pneumonia, among others. Worldwide, more than 29million confirmed COVID-19 cases have been reported with 926,544 deaths, 51% of which correspond to the Americas. Careful observations have hypothesized that patients present with different clinical patterns that depend mainly on 3 factors: (1) severity of infection and host response, physiological reserve and comorbidities (2) ventilatory response to hypoxemia and (3) the delay from the onset of symptoms and evaluation in the hospital. About 4.4% of patients require IMV during the first 14days after symptoms start and reach a high mortality rate. This disease mainly shows two behaviors related to time: phenotype L, Low elastance [high compliance] and phenotype H, High elastance [low compliance]. The L phenotype, with low V/Q ratio, low lung weight, and low potential for recruitment occurs early in the disease. The H phenotype is characterized by low compliance, high shunt levels, high lung weight, and high potential for recruitment, and it usually manifests within 7days. In our experience, there would be a third group that progresses to early pulmonary fibrosis characterized by very low compliance, making the ventilatory process exceedingly difficult (they require a low PEEP [6-8cmH2O] and very low VT 4-6ml/kg predicted body weight. These patients retain CO2 and may require extracorporeal CO2 removal (ECCO2R). Although SARS CoV-2 pneumonia does not evolve as a classic ARDS, emerging evidence suggests that ARDS associated with CoVID-19 evolves with acute respiratory failure and lung mechanics typical of a historical ARDS. One aspect that could differentiate them is related to the levels of D-Dimer (DD). The subgroup of patients with DD concentrations higher than the median and a static compliance equal to or less than the median (HDLC: High D-dimers, low compliance) have at 28-days mortality higher than the rest of the groups, such as: high DD with high compliance (HDHC), low DD with low compliance (LDLC) and low DD with high compliance (LDHC). The 28-day mortality for HDLC was 56% and 27% for LDHC Up to the present time, IMV with open lung approach (OLA) has not been shown to reduce mortality; it has only accomplished to improve oxygenation and reduce driving pressure, without exerting deleterious effects such as barotrauma or increases in mortality.